Synthetic lubricant composition and process

ABSTRACT

A liquid polymer suitable for use as a lubricant base oil is produced by polymerizing ethylene and at least one alpha-olefin using a metallocene catalyst to provide a polymer which is then isomerized and hydrogenated to produce the liquid polymer.

This application is a Continuation-In-Part of U.S. Ser. No. 10/663,567filed Sep. 16, 2003 now U.S. Pat. No. 7,022,784 which is based on U.S.Provisional Application 60/421,317 filed Oct. 25, 2002.

FIELD OF INVENTION

The present invention relates to ethylene-alpha olefin copolymers, theirmethod of preparation and use as a lubricating oil.

BACKGROUND OF THE INVENTION

Mechanical devices, such as internal combustion engines, require the useof a lubricant to protect mechanical parts from wear, to promotefriction reduction, to inhibit rust and the like. Indeed, todayautomotive engines are designed to operate at higher temperatures thanin even the recent past and these higher operating temperatures requirehigher quality lubricants.

One of the requirements for lubricants for use in currently designedengines is for higher viscosity indices (VI's) in order to reduce theeffects of the higher operating temperatures on the viscosity of theengine lubricants.

Poly alpha olefins (PAO's) produced by polymerizing linear alphaolefins, especially C₈ to C₁₂ linear alpha olefins have excellent VI'sand consequently have found use as lubricant base oils. Unfortunately,linear alpha olefins are expensive and often in short supply, therebylimiting the use of PAO's in lubricant compositions. Therefore, there isa need for synthetic base oils that are less expensive than PAO's andthat have equivalent or better properties.

Olefins such as ethylene, propylene and butene are available in largequantities at relatively low cost. Thus, producing base oils from thesenonomers offers the potential as a low cost alternative to PAO's.Attempts to form base oils by copolymerizing ethylene with an alphaolefin having at least 3 carbon atoms has not led to entirelysatisfactory products. Typically, liquid ethylene/alpha olefincopolymers have poor pour points and cloud points, and are often hazy.

Thus, there remains a need for synthetic base stocks that have highVI's, e.g., greater than about 110 and good low temperature propertiessuch as pour point, cloud point and are haze-free.

SUMMARY OF THE INVENTION

Accordingly in one embodiment the present invention provides a processfor producing a liquid polymer from ethylene and at least one alphaolefin suitable for use as a lubricant base oil comprising:

(a) polymerizing ethylene and at least one alpha olefin in the presenceof a metallocene catalyst system under conditions sufficient to producea liquid polymer;

(b) isomerizing the liquid polymer in the presence of an acidicisomerization catalyst to produce an isomerized liquid polymer; and

(c) hydrogenating the isomerized liquid polymer in the presence of ahydrogenating catalyst to produce an isomerized liquid ethylene-alphaolefin polymer suitable for use as a lubricant base oil.

The novel polymers produced according to the invention may becharacterized as follows:

(a) an ethylene unit content of 0.1 to 85 weight %;

(b) an alpha-olefin unit content of 15 to 99.9 weight %;

(c) a mixed head to tail and tail to head molecular structure;

(d) a pour point below about −15° C.; and

(e) a cloud point of not more than +20° C.

Other embodiments of the invention will become apparent from thedescription and examples which follow:

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the present invention is directed toward polymers derivedfrom ethylene and at least one alpha olefin. These polymers havephysical properties which makes them particularly useful as base oilsfor lubricants. Although the alpha-olefins from which the copolymers arederived may have from 3 to 24 carbon atoms, advantageously the polymersare especially derived from ethylene and alpha-olefins having 3 and 4carbon atoms. The polymers produced in accordance with the presentinvention have viscosity indices (VI's), pour points and cloud pointsthat contribute to the usefulness of the polymer as a lubricant baseoil.

In another aspect, the invention is directed toward a process forproducing an ethylene-alpha olefin polymer comprising the steps of:polymerizing ethylene and one or more alpha olefins having 3 to 24carbon atoms in the presence of a metallocene catalyst system;isomerizing the resulting polymer in the presence of an isomerizationcatalyst and thereafter hydrogenating the isomerized polymer in thepresence of the hydrogenation catalyst.

(a) The Polymerization Step

The copolymerization may be carried out in a batch or continuous manner,in the presence or absence of a solvent, using a metallocene catalystsystem. Such catalyst systems are well known in the art and comprise atransition metal compound of Group IVb of the Periodic Table of theElements such as Ti, Zr and Hf; and an aluminoxane co-catalyst.Specifically, useful transition metal compounds are disclosed, forexample, in U.S. Pat. Nos. 5,498,809 and 6,124,513 and incorporatedherein by reference.

The aluminoxane co-catalyst are polymeric aluminum compounds typicallyemployed as co-catalysts in metallocene catalyst systems. Specificuseful examples are disclosed in the aforementioned U.S. patentsincorporated herein by reference.

The ethylene/alpha olefin feed will comprise 0.1 to 85 wt % of ethyleneand from 15 to 99.9 wt % of at least one alpha olefin having from 3 toabout 24 carbon atoms acid especially from 3 to 18 carbon atoms.

The source of the alpha olefins can be from any petrochemical plant, orfrom dilute alpha-olefin-containing refinery streams, include butene-1from Raffinate-2, and propylene. Most preferred is the polymerization ofethylene with butene-1 or propylene in a dilute refinery stream.

As previously stated, the process of the present invention utilizes ametallocene catalyst system. Such metallocenes are extremely unreactivewith non-terminal olefins, and terminal olefins which lack at least onehydrogen atom on the second carbon (e.g., isobutylene), at least twohydrogens on the third carbon (e.g., isopentene). Hence, as describedhereinafter, many of the components in refinery streams, such asRaffinate-1 stream, which contains 1-butene, 2-butene, and isobutylenein butanes, are suitable for use as starting material, as the 2-butenesand isobutylene are essentially non-reactive in a metallocene system andbecome suitable diluents for use in the present process, and thesecomponents need not be separated from the feed. Similarly, Raffinate 2stream available from a polyisobutylene plant or the Raffinate streamfrom a methyl t-butylether (MTBE) plant, which contains mostly 1- and2-butenes in butanes, typically 10-70% butanes, 15-85% 1 and 2-butenesand less than 5% isobutylene, is also suitable. This Raffinate 2 streamis more preferred. Other constituents such as 1,2-butadiene may be madenon-reactive by pre-saturating the double bonds with hydrogen or removedby feed pretreatment. All the feeds that go into the polymerizationreactor are usually purified by passing through molecular sieve bed,solid sorbant bed consisting of activated aluminas, or solidde-oxygenation catalyst. All these beds can be used individually or incombination. These beds remove the oxygenates, polar poisons, dienes,and all other undesirable components which may deactivate thepolymerization catalyst.

When conducted in the presence of a solvent, any liquid inert underreaction conditions may be used. Suitable solvents include paraffins,such butane, isobutane, pentane, hexane, Norpar solvent or Isoparsolvent, etc., aromatic solvents, such as benzene, toluene, xylenes,ethylbenzenes or mixture of them. Usually the preferred solvent istoluene and butane, isobutane or paraffins that are already present inthe feed.

The polymerization reaction is conducted in the temperature range offrom about 0° C. to about 250° C., preferably from about 25° C. to about200° C. in the substantial absence of molecular hydrogen and atpressures in the range of about 7 kPa to about 13.79 MPa (about 1 psi toabout 2,000 psi) and preferably about 103 kPa to about 6.895 MPa (about15 psi to about 1,000 psi).

The resulting polymer is a viscous liquid having considerableunsaturation as measured by bromine number and a substantially head totail molecular structure as exemplified by formula I for anethylene-butene copolymer

In the course of polymerization, the alpha-olefin comonomer can add inthe head to tail configuration (also referred to as 1,2-addition)described in the preceding paragraph, or it can add in a regio-invertedconfiguration (referred to as 2,1-addition). This can give rise to shortchain branches on adjacent carbons (head to head configuration), ortertiary backbone carbons separated by an even number of interveningmethylenes. The case with two intervening methylenes is referred to astail to tail addition.

(b) The Isomerization Step

The liquid polymer is next subjected to isomerization. Isomerization, ofcourse, results in the rearrangement of the molecular structure and isachieved in the substantial absence of hydrogen and in the presence ofan isomerization catalyst. Any known acid isomerization catalyst may beused. The acid catalyst can be the typical homogeneous acid catalysts,such as AlCl₃, BF₃ (halides of Group IIIA) or modified form of thesecatalysts, or other typical Friedel-Crafts catalysts, such as thehalides of Ti, Fe, Zn, and the like. The acid catalyst can be solidmetals or metal oxides or their mixture of Group IVB, VB, VIB and GroupIII; or the metal oxides or mixed oxides of Group IIA to VA; or othermixed metal oxides such as WO_(X)/ZrO₂ type catalyst, or solid naturalor synthetic zeolites, layered material, crystalline or amorphousmaterial of silica, alumina, silicoaluminate, aluminophosphate,aluminumsilicophosphate, etc. These solid acidic catalysts may containother Group VIII metals such as Pt, Pd, Ni, W, etc., as promoters.Generally, it is preferred to use a solid, regenerable catalyst forprocess economic reason and for better product quality. The preferredcatalysts include: ZSM-5, ZSM-11, ZSM-20, ZSM-22, ZSM-23, ZSM-35,ZSM-48, zeolite beta, MCM22, MCM49, MCM56, SAPO-11, SAPO-31, zeolite X,zeolite Y, USY, REY, M41S and MCM-41, WO_(X)/ZrO₂, etc. The solidcatalyst can be used by itself or co-extruded with other bindermaterial. Typical binder material includes silica, alumina,silicoalumina, titania, zirconia, magnesia, rare earth oxides, etc. Thesolid acidic catalyst can be further modified by Group III metals, suchas Pt, Pd, Ni, W, etc. Sometimes the zealots can be modified by hightemperature steam treatment or by chemical treatment to reduce theactivity for side reactions, such as cracking, cyclization oraromatization, etc. These modifications can be carried out before orafter co-extrusion with binder material. Sometimes the metalmodification provides improvement in activity, sometimes it is notnecessary. Typical discussion of catalysts and their preparation can befound in U.S. Pat. No. 5,885,438 which is incorporated herein byreference.

The isomerization can be carried out in fixed-bed, continuous operation,in batch type operation or in continuous stir tank operation. Generallythe residence time ranges from a few seconds to up to one or two daysdepending on reaction temperature, catalyst activity and catalystparticle size. For economic reasons, it is prefer to have shorterresidence time and yet accomplish enough isomerization to give improvedproperties. Usually, residence time of 10 minutes to 20 hours residencetime is suitable.

The isomerization is conducted at temperatures in the range of about100° C. to about 400° C. and preferably at about 125° C. to about 300°C. and at pressures of about 0 kPa to about 13.79 MPa (about 0 psi toabout 2,000 psi) and preferably about 35.5 kPa (about 15 psi)(atmospheric pressure) to about 6.895 MPa (about 1,000 psi).

(c) The Hydrogenation Step

The isomerized polymer is next subjected to hydrogenation in thepresence of a hydrogenation catalyst. Hydrogenation catalysts are wellknown in the art and include Group III metals supported on inertsupports such as carbon, kieselgel, clay, alumina, crystallinemicroporous material and the like. The commonly used hydrogenationcatalyst is Ni on kieselgel or Pt or Pd on alumina.

Hydrogenation is conducted at temperatures in the range of about 100° C.to about 350° C., preferably about 150° C. to about 250° C., and athydrogen pressures of about 103 kPa to about 13.79 MPa (about 15 psi toabout 2,000 psi), preferably about 138 kPa to about 6.895 MPa (about 20psi to about −1,000 psi). Generally, the isomerized polymer ishydrogenated to give a bromine number of less than 2. In some specialapplications where it is desirable to produce a product with a brominenumber less than 0.1, more severe hydrogenation conditions or a moreactive catalyst may be necessary. As is known, a lower bromine numberfor the polymer typically is beneficially for improved oxidativestability.

The isomerized and hydrogenated polymer is characterized by a mix ofhead to tail, tail to tail, and/or head to head as exemplified byformula II for an ethylene-butene copolymer. As will be appreciated, ifother alpha-olefins were used in the polymerization step, the C₂H₄ groupin the structure will correspond to the other alpha-olefins.

In this structure, the Rs are alkyl groups which are mostly CH₃ groups,with some being ethyl, n-propyl or iso-propyl groups and in much lowerquantity. These extra alkyl groups result from the isomerization step.

c) The Polymer Products

The isomerized polymer products useful as lubricant base oils typicallywill have number-averaged molecular weight in the range of about 200 toabout 20,000. The molecular weight distribution ranges from 1.01 to 4,most common distribution range from 1.2 to 3.0. These lube base oil have100° C. viscosities ranging from 2×10⁻⁶ to 5×10⁻³ m²/sec (2 to 5,000cSt). The most commonly used viscosity range is from 3.5×10⁻⁶ to 5×10⁻³m²/sec (3.5 cSt to 1,000 cSt. In general the products also will haveVI's greater than about 100, typically greater than 120, pour pointsbelow about 0° C. for example from below −15° C. and cloud points belowabout 25° C. and preferably less than 20° C.

NMR spectroscopy provides key structural information about thesynthesized polymers. Carbon-13 NMR can readily be used to determine themonomer composition of the polymer, as well as the concentration ofbranch types, and blocks of contiguous backbone methylenes more thanthree carbons from a branch point or four carbons from a chain end.Spectra for a PAO sample are acquired in the following manner.Approximately 100-1000 mg of the PAO sample is dissolved in 2-3 ml ofchloroform-d containing approximately 15 mg/ml (solvent basis) ofchromium acetylacetonate relaxation agent, Cr(acac)₃, to enhance thedata acquisition rate, and tetramethylsilane (TMS) for chemical shiftreferencing. Free induction decays are acquired with a 90-degree carbonpulse, inverse-gated proton decoupling, and a total pulse-to-pulse delayof greater than 3 seconds. The chemical shift range is referenced bysetting the TMS peak to 0.0 ppm. The relevant integration regions forthe branch types are: methyl (21-18.6 ppm), ethyl (12.8-9.5 ppm), propyl(14.8-14.3 ppm), butyl (14.3—approximately 14.12 ppm), andpentyl-and-longer (approximately 14.12 ppm—13.9 ppm). The polymethyleneresonances are integrated from 29.95-29.65 ppm.

EXAMPLE 1

This example illustrates the copolymerization step of the presentinvention.

In this example polymer grade ethylene, polymer grade 1-butene andpolymer grade iso-butane solvent were charged into a 200 gallon reactorafter purification through molecular sieve and treatment by injecting 50ppm tri-t-butylaluminum. The feed rates for ethylene, 1-butene andiso-butane were 26, 54, and 128 kg/hour (58, 120 and 283 lb/hour),respectively. A catalyst solution, containing 5×10⁻⁶ g-mole/liter ofdimethylsilylbis (4,5,6,7 tetrahydro-indenyl) zirconium dichloride andmethylaluminoxane of 1/400 Zr/Al molar ratio in toluene, was chargedinto the reactor at 13.5 mL/minute. The reactor temperature wasmaintained between 98 and 101° C. (209 and 214° F.), pressure 2.00-2.07MPa (290-300 psi) and average residence time 1 hour. The crude reactionproduct was withdrawn from the reactor continuously and washed with 0.4wt % sodium hydroxide solution followed with a water wash. A viscousliquid product was obtained by devolitalization to remove iso-butanesolvent, light stripping at 66° C./30 kPa (150° F./5 psig) followed bydeep stripping at 140° C./1 milliTorr. This viscous liquid was used forfurther experiments.

EXAMPLES 2 TO 5

These examples illustrate the isomerization and hydrogenation steps ofthe present invention and the increased branchiness achieved thereby.

In Example 2, one hundred grams of the viscous liquid prepared inExample 1 was mixed with two grams of a powdered platinum (0.6 wt %)modified ZSM-48 catalyst and heated to 260° C. under nitrogen atmospherefor 16 hours. The catalyst was then filtered off. The filtrate was thenmixed with 2 wt % of a 50% nickel on kieselgel catalyst, heated to 200°C. under 5.52 MPa (800 psi) H₂ pressure for 16 hours. The hydrofinishedviscous liquid, after separation from the catalyst, was distilled at150° C., <1 milliTorr vacuum for two hours to remove any light ends,usually less than 3%.

In Example 3 to 5 the procedure of Example 2 was followed except theisomerization was conducted at 275° C., 300° C. and 320° C.respectively.

The properties of the final lube product for Examples 2 to 5 are listedin Table 1.

COMPARATIVE EXAMPLE 1

This example illustrates that hydrogenation of the copolymer withoutisomerization results in a product with inadequate cloud point.

In the comparative example, a 100 gram sample of the residual viscousliquid was hydro-finished at 200° C., 5.52-8.274 MPa (800-1200 psi) H₂pressure with 2 wt % Ni-on-Kieselguhr catalyst for eight hours. Thefinished lube base stock contains 44 wt % ethylene and has the followingproperties: 100° C. KV=1.499×10⁻⁴ m²/sec (149.9 cSt), 40° C.KV=2.4184×10⁻³ m²/sec (2418.4 cSt), VI=164, Pour point=−24° C., Cloudpoint =+45° C. The properties of this material are given in Table 1.

TABLE 1 Example No. Comp. 1 2 3 4 5 Isom. Temperature, Not 260 275 300320 ° C. applicable 100° C. Visc. cSt 149.9 147.4 155.0 160.1 157.4 40°C. Visc. cSt 2418.4 2279 2466 2618 2603 VI 164 167 167 166 164 PourPoint, ° C. −24 −24 −24 −23 −23 Cloud Point, 42 −7 −7 −10 −11 ° C. (a)C₁ branch/1,000 C. 10.2 10.5 10.5 11.3 24.0 C₃ branch/1,000 C. 1.0 1.31.5 2.5 5.4 C₄ branch/1,000 C. 2.7 2.7 2.6 3.0 4.4 C₅₊branch/1,000 C.5.5 5.8 6.3 6.3 7.2 (CH₂)_(x) at 29.9 ppm 96.4 93.7 94.1 94.7 86.0 Totalshort chain 19.4 20.3 20.9 23.1 41.0 branches (b) (a) - measured by ASTMD2500 method (b) - include C₁ to C₅ and higher branches

EXAMPLE 6

This example further illustrates the process of the invention.

In this example a sample of the viscous liquid prepared in Example 1 wasfed from a high pressure syringe pump at 2 mL/hour into a fixed bedmicroreactor, containing two grams of a platinum-modified ZSM-48catalyst, heated to 285° C. and pressurized to 5.52 MPa (800 psi). Theeffluent, together with hydrogen gas of 8.33 mL/hour, was then fedthrough the second fixed bed reactor, containing four grams of a 50 wt %nickel on Kieselguhr catalyst at 250° C. and 5.52 MPa (800 psi). Thefinal product from the reactor system was collected every 48 hours. Theliquid crude product was then distilled at 150° C./<1 milliTorr vacuumfor two hours to remove light ends. Usually, the lube yields were veryhigh >95% and less than 5 wt % of distillates was collected. The lubeproduct properties and compositions were summarized in Table 2. Thesedata demonstrated that the cloud point of the sample was reduced from42° C. to less than 15° C. by treatment with Pt-ZSM-48.

TABLE 2 Products Starting Material 1 2 3 4 5 6 Days on Stream 4 8 12 1620 22 Lube yield by 97.1 96.8 96.6 94.6 95.3 96.2 distillation, wt %Lube Properties 40° C. Visc, cSt 2418.4 2609 2507 2549 2583.67 2548.422345.89 100° C. Visc, cSt 149.85 161.3 155.0 158.3 164 163.5 152.16 VI164 161.3 165.0 166.5 166 167 165 Pour Point, ° C. −24 −22.3 −22.9 −22.3−23 −23.5 −23.1 Cloud Point, ° C. +42 <15 <15 <15 <15 <15 <15 ProductAppearance Hazy Clear Clear Clear Clear Clear Clear

EXAMPLE 7

An ethylene-butene co-polymer was prepared by charging a mixed butenefeed containing 60 wt % 1-butene and 40 wt % 2-butene at 100 mL/hour,hydrogen at 20.5 mL/minute and ethylene at 24 gram/hour into a 600 mLautoclave containing a catalyst solution of 55 mg zirconocenedichloride, 0.4 gram methylaluminoxane and 50 gram toluene, and cooledin a water bath at 20° C. The feeds were discontinued after three hours.After 2 hours of reaction at 30° C., the reaction was quenched withwater and alumina. The catalyst and any solid was removed by filtration.The viscous liquid product was isolated in distillation at 140° C./0.1milliTorr for 2 hours to remove any light ends. This fluid washydrogenated to remove any unsaturation. After hydrogenation the fluidhad the following properties: 100° C. KV=1.192×10⁻⁵ m²/sec (11.92 cSt),40° C. KV=7.281×10⁻⁵ m/sec (72.81 cSt) and pour point=−22° C. Incontrast, when the unhydrogenated polymer is treated with 2 wt %Pt-ZSM-48 catalyst at 275° C. followed by hydrogenation in a similarmanner as Example 2 the resulting fluid had the following properties:100° C. KV=1.497×10⁻⁵ m²/sec (14.97 cSt), 40° C. KV=1.098×10⁻⁴ m²/sec(109.8 cSt) and pour point=−45° C. This data shows that the polymerafter zeolite treatment has a significantly improved pour point and ishaze-free.

1. An isomerized ethylene-butene-1 copolymer comprising: (a) an ethyleneunit content of 0.1 to 85 wt %; (b) a butene-1 unit content of 15 to99.9 wt %; (c) an amount of methyl branches per 1000 carbon atoms ofgreater than or equal to 10.5 and less than or equal to 24.0 asdetermined from methyl branch resonances in the 18.6-21 ppm range viaCarbon-13 NMR spectroscopy; and (d) wherein the ethylene-butene-1copolymer has a cloud point of not more than 20° C.
 2. The copolymer ofclaim 1 wherein the copolymer has a pour point below 0° C.
 3. Thecopolymer of claim 1 wherein the copolymer has a number-averagedmolecular weight in the range of 200 to 20,000.
 4. The copolymer ofclaim 1 wherein the copolymer has a bromine number less than
 2. 5. Thecopolymer of claim 1 wherein the copolymer contains more methyl branchesthan an unisomerized copolymer with a similar butene-1 content made by asame process excepting isomerization.
 6. The copolymer of claim 1wherein the copolymer contains more ethyl branches than an unisomerizedcopolymer with a similar butene-1 content made by a same processexcepting isomerization.
 7. The copolymer of claim 1 wherein thecopolymer contains more propyl (C₃) branches than an unisomerizedcopolymer with a similar butene-1 content made by a same processexcepting isomerization.
 8. The copolymer of claim 1 wherein thecopolymer contains more butyl (C₄) branches than an unisomerizedcopolymer with a similar butene-1 content made by a same processexcepting isomerization.
 9. The copolymer of claim 1 wherein thecopolymer contains more pentyl (C₅) branches than an unisomerizedcopolymer with a similar butene-1 content made by a same processexcepting isomerization.
 10. The copolymer of claim 1 wherein thecopolymer contains a higher concentration of short chain branches thanan unisomerized copolymer with a similar butene-1 content made by a sameprocess excepting isomerization.
 11. The copolymer of claim 1 whereinthe copolymer contains a lower concentration of (CH₂)_(x) units than anunisomerized copolymer with a similar butene-1 content made by a sameprocess excepting isomerization.